Firing mechanism for an automatic firearm



May 19, 1959 w. R. KuNz 2,887,012

FIRINGv MECHANISM FOR AN AUTOMATIC FIREARM Filed Aug. 21, 1957 2Sheets-Sheet 1 Il/Illlllll IIWIII INVENTOR.

/l/l/ william R -Kunz /////[llll1 BY Y K May 19, 1959 2 sheds-sheet 2INVENTOR mim @www

United StatesPatent FIRING MECHANISM FOR AN AUTOMATIC FIREARM William R.Kunz, Springfield, Mass., assigner to the United States of America asrepresented by the Secretary of the Army `Application August 21, 1957,Serial No. 679,802

5 Claims. (Cl. 89-131) (Granted under Title 35, U.S. 'Code (1952), sec.266) 'Ilhe invention vdescribed herein may be manufactured and used byor for the Government for governmental purposes without the payment ofany royalty thereon.

This invention relates to automatic firearms and more particularly tofiring mechanisms therefor whereby a firearm may be selectively adjustedto fire a single round, short'bursts of a predetermined number ofrounds, or continuously.

`It is one of the objects of this invention to provide for automaticfirearms a firing mechanism through which a 2,887,012 lieferte@ .Mer1,91959 ceiver 12 and is provided with a pair of laterally-spaced of thebolt when moving to recoil position. Hammer firearm may be operated atthe optimum'rate to obtain the maximum benefits from continuous fireat-a high rate, while being conservative in the 'expenditure ofammunition, with the continuous operation being automatically stoppedafter a predetermined burst quicker than is possible through manualrelease of the operating trigger.

j It is another object of this invention to provide for firearms whichutilize a hammer-activated firing p-in to fire a chambered cartridge, afiring mechanism whereby s'uch a` firearm may be fired continuously aslong as the trigger is held in firing position or which automaticallyinterrupts the operation of the firearm after'a single round has beenfired or after a short burst of a. predetermined number of rounds.

' It is a further object of this invention to provide for such firearmsa firing mechanism in which a Geneva device cooperates with the hammerin controlling the num- I ber of rounds fired while the trigger is heldin firing position.

It is still another object of this invention to provide for 'such afiring mechanism a selector which serves both to move a coupler intoselective relationship with the Geneva device and to selectively blockthe movement of the Geneva ydevice and thereby act as a safety by makingthe firearm inoperative. i

' It is another and still further object of this invention to providefor such a firing mechanism a device for safetying the vfirearmregardless of whether the hammer is in .firing or cock position.

It is still another and further object of this invention to provide afiring mechanism for selectively adapting a firearm to a number ofoperating conditions and which is simple and rugged in constructionv andpositive in operation.

The specific nature of the invention las well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown inthe 'accompanying drawings in which: Fig. l is apartially cross-sectioned side view of the firearm showingthe selectorin Safe position;

Fig. 2 is the same as Fig. l but showing the hammer retracted by thebolt, the trigger in the retracted position and the selector indexed forlimited burst ring; l

Fig. 3 is an enlarged viewtaken along line 3-3 of Fig. 4; Y l

Fig. 4 is -the same vas Fig. 1 butshowing-.the trigger. in

24 -is maintained in retracted position during movement of the bolt 14to and from recoil position by the sliding engagement of free end 26with the bottom side of the bolt. vA :spring 28 biases hammer 24 to thefiring position.

A trigger 30 is pivotally mounted in trigger housing 18 on a pin 32which extends transversely through the trigger housing to the rear ofand below pin 22. Trigger 30 includes a finger portion 34 which extendslbelow trigger housing 18 and a sear arm 36 which extends forwardly toengage a catch port-ion 38 in hammer 24 for releasably holding thehammer in a cock position between the re tracted and firing positionsthereof. Trigger 30 also includes a selector arm 40 which extendsupwardly from pin 32. A spring 42 is disposed between sear arm 36 andthe bottom of trigger housing 18 so as to bias finger portion 34 tonormal forward position and such scar arm upwardly into hammer engagingposition. Upward movement of Sear arm 36 is limited Aby the rearwardengagement of selector arm 40 with a rod 43 extending transverselythrough trigger housing 18.

-A Geneva device 44 is rotatably mounted in trigger housing 18 betweenhammer 24 and selector arm 40 on a transversely disposed axle 46 so asto be engaged for rotation by hammer 24 during pivotal movement thereof,as hereinafter explained. Geneva device 44 includes a gear wheel 48which is substantially square in configuration and is provided with foursides 50 which are arcuately recessed to form four teeth 52 at thecorner portions. Such Geneva device also includes a sprocket wheel 54with a single sprocket 55 which abuts gear wheel 48 on n one of thesides 20.

The arcuately formed sides 50 of gear wheel 48`have a radius similar tothat of the outside perimeter of hammer 24 and such gear wheel andhammer are so related that the outer perimeter of the hammer and one ofthe sides of the gear wheel are in contiguous sliding relationshipduring movement of such hammer between the firing and cock positionsthereof. As axle 46 is mounted through trigger housing 18 above pin 22,the teeth 52, which are in the two upper positions, are posistioned inparallel alignment with a line through the centers of such axle and pinduring the sliding engagement of one of the sides 50 with hammer 24.Consequently, the rear one of the upwardly disposed teeth 52 extendsabove the front one thereof when hammer 24 is in engagement with one ofthe sides 50.

' Extending radially outward from fr'eeend 26 is a sub-` staar/piastantially triangular lug portion S8 disposed for camming engagementwith the forward one of the upwardly disposed teeth 52 during movementof hammer 24 from cock to retracted position. Lug portion 58 is sorelated to gear wheel 48 that the camming engagement therebetweenrotates the gear wheel in a counterclockwise direction until thc upperones of the teeth S2 are in parallel alignment with the longitudinalaxis of the firearm and out of the path of movement of bolt 14. It isevident that as the forward one of the upwardly-disposed teeth 52 isrotated upwardly, the forward one of the lower-most teeth is rotatedforwardly and is received by a recess 60 extending into hammer 24.Recess 60 forms a cog portion 62 which is engageable with the one of theteeth 52 which is rotated into such recess during movement of hammer 24from retracted to cocked position so that gear wheel 48 continues to berotated in a counterclockwise direction to bring such gear wheel andhammer into sliding engagement during the remaining movement of thehammer to tiring position. Consequently, during an operational cycle ofthe firearm, Geneva device 44 is rotated 90 by hammer 24 when pivoted toand from retracted position. Furthermore, when gear wheel 48 is heldagainst rotation, by means as hereinafter explained, the engagement ofcog portion 62 with such gear wheel 48 blocks the movement of hammer 24to cock position.

A shaft 64 is mounted transversely through trigger housing 18 so as topass in front of selector arm 40 at `the junction thereof with sear arm36. Mounted on shaft 64, as hereinafter described, is a coupler 66provided with a hub portion 68 which receives shaft 64, and an armportion 70 which extends upwardly from the hub portion between selectorarm 40 and Geneva device 44 so that the free end of such arm portion isengageable with the rear one of the uppermost teeth 52 when engageablypivotcd forwardly by selector arm 40. A coil spring 72 is operationallydisposed between hub portion 68 and trigger housing 18 for torsionallybiasing coupler 66 in a counterclockwise direction and linearly biasingsuch coupler along shaft 64 into normal contact with the left one of thesides 20. Whereby, arm 70 is normally aligned with spacer 56 and isslidable along shaft 64 into alignment with gear wheel 48 and sprocketwheel 54.

Coupler 66 is movable into selective alignment with gear wheel 48 andsprocket wheel 54- by a selector 76 which is iixedly mounted to arotatable shaft 74 mounted transversely through trigger housing 18.Selector 76 includes a cylindrical hub portion 78 having an axial holetherethrough for receiving shaft 74 as by press fit. An arcuate camportion 80 extends radially from hub portion 78 for cooperation, ashereinafter described, with a foot portion 82 extending forwardly fromhub portion 68.

Cam portion 80 develops angularly, as hereinafter described, in acounterclockwise direction from a leading edge 86 which extends radiallyfrom the left end of hub portion 7S. Extending angularly to the right,respective to the gun, and in a counterclockwise direction from leadingedge 86, is a primary ramp portion 84 which leads to a planar primarystep portion 83 disposed parallel to the longitudinal plane of thefirearm. A secondary ramp portion 90 extends similarly from primary stepportion 88 to a secondary step portion 92 disposed parallel to primaryramp portion 8S. Provided on the left side of foot portion 82 is anangular surface 94 which is cammingly engageable by primary ramp portion84 and secondary ramp portion 9) to translate counterclockwise rotationof selector 76 to lateral movement of coupler 66 towards the right oneof the sides 20. Primary and secondary portions 88 and 92 are sodisposed that, when in engagement with foot portion 82, arm portion 70is in engageable alignment with gear wheel 48 and sprocket wheel 54,respectively.

Selector 76 is also disposed relative to Geneva device 44 so that, whenthe perimeter of secondary `step portion 92 is moved to its uppermostpositionas' shown in Fig. 1,

gear wheel 48 is engageably blocked from counterclockwise rotation andso acts as a safety to prevent operation of the rearm. When selector 76is in such Safe position, gear wheel 48 is engageably positioned therebyso that the upper ones of the teeth 52 are disposed parallel to thelongitudinal axes of the rearm. VVhereby, hammer 24 is free to pivotfrom tiring to retracted position but is blocked during movement fromretracted to cock position. Thus, it is evident that the firearm may bemade Safe even when hammer 24 is in firing position as is not possiblein most rearms.

Shaft 74 is arranged to extend beyond the right one of the sides 20, andmounted to such extending portion is a radially disposed lever 96 bywhich selector '76 may be rotated manually. Provided in the free end oflever 96 is a detent 98 which is spring-biased against the face of theadjacent one of the sides 20 and is releasably received by one of fourindexing indentations 100 in such side. Such indentations 10@ arearranged to successively receive detent 93 when selector 76 is inalignment with spacer S6, when foot portion 82 is in respectiveengagement with. the primary and secondary step portions 88 and 92, andwhen the selector is in Safe position. The indexing indentations 100 aresuitably marked to show the operating condition to which the firearm isselectively regulated.

An automatic Sear 102 is mounted on the outside of the left one of thesides 20 for sliding movement between a rearward lock position and aforward unlock position. Automatic scar 102 is provided with a lockportion 104 which extends into trigger housing 18 through a longitudinalslot 106. Automatic scar 102 is spring-biased by means (not shown) tolock position and is actuated to the unlock position by the operatingmechanism (not shown) of the firearm when bolt 14 is locked in batteryposition. Lock portion 104 cooperates with a notch 108 extending intohammer 24 from the inside perimeter thereof for releasably locking thehammer in a lock position between the cock and firing positions untilbolt 14 is locked in battery position, at which time automatic sear 102is actuated to release hammer 24, if in engagement therewith, or ismoved out of the way for uninterrupted movement of the hammer to tiringposition when released from engagement with sear arm 36.

Operation.

To regulate the firearm for ring only a single round each time trigger30 is actuated, lever 96 is rotated to the one of the indexingindentations 100 whereby coupler 66 is moved by selector 76 intoposition for arm portion 70 to be engageably aligned with gear wheel 48.Thus, starting with the firearm charged so that hammer 24 is engaged incock position by sear arm 36, such sear arm is disengaged from catchportion 38 to release the hammer for engagement with ring pin 16 to lirethe chambered cartridge when trigger 30 is actuated to firing position.During the initial movement of hammer 24 from cock position, the one ofthe teeth 52 which is received by recess 60 and engaged by cog portion62 is rotated upwardly and in a connterclockwise direction by such cogportion until the following one of the sides 50 and the outsideperimeter of hammer 24 align for sliding engagement during the remainingtravel of the hammer to tiring position.

As bolt 14 recoils responsive to the discharge, hammer 24 is actuatedthereby to retracted position. When hammer 24 approaches retractedposition, lug portion 58 thereon cammingly engages the one of the teeth52, moved by cog portion 62 upwardly during rotation of the hammer totiring position, to continue the counterclockwise rotation of gear Wheel48 until such tooth is in longitudinal alignment, respective to thefirearm, with the other one of the upwardly-disposed teeth. Consequentlythe next one of the teeth 52 is moved into recess 60 in position .to beengaged by cog portion 62 when hammer 24 pivots-from retracted positionwith the-counterrecoil of bolt 14. With trigger 30 in firing position,coupler 66 is pivoted forwardly by selector arm 40 into position to beengaged by the rearward one of the uppermost teeth 52. Consequently,gear wheel 48 is blocked from rotation and thereby, because of theengagement of cog portion 62 with the one of the teeth 52 received byrecess 60, hammer 24 is prevented from proceeding Vto cock position.When trigger 30 is permitted to return to normal position, the movementof selector arm 40 is in a counterclockwise direction and away fromcoupler 66 to unblock gear wheel 48 which is now free to be rotatedthrough the bias of hammer 24 to where catch portion 38 and sear arm 36become engaged to releasably hold the hammer in cock position, when thetrigger reaches normal position. Thus, when bolt 14 is locked inbatteryposition and automatic scar 102 consequently moved to unlockposition, the lirearm may be operated to re another round when trigger30 is reactuated.

` If the r'earm is to be operatedin automatically limited bursts, lever96 is rotated in a clockwise direction to the next oneof the indexingindentation; 100. Whereupon, the camming engagement of secondary rampportion 90 with angular surface 94 moves coupler 66 along shaft 64untiljsecondary step portion 9,2 is in engagement with foot portion 82,and arm portion 70 is engageably aligned with sprocket wheel 54.Thereby, when trigger 30 is actuated, the action of the firing mechanismwill be similar to that described above except that firing will continueuninterruptedly through the cooperation of automatic sear 102 withhammer 24 until sprocket wheel 54 is rotated through the cooperation ofthe hammer and gear wheel 48 into engagement with coupler 66 heldforwardly by trigger 30. Whereupon, ring will be automatically stoppedbut may be resumed for another burst after trigger 30 is returned tonormal position, because through the return of the trigger to normalposition with resulting movement of hammer 24 to cocked position, thepreviously engaged one of the teeth 52 is rotated past the position tobe engaged by coupler 66, and the control of the hammer is transferredfrom Geneva device 44 to sear arm 36.

It is apparent that the number of rounds in the burst depends upon thenumber of firing cycles required to rotate sprocket wheel 54 in acomplete revolution. In the present embodiment, Geneva device 44 isrotated 90 during each operating cycle, but it is apparent that this maybe varied by changing the number of teeth provided on the gear wheel andmaking the necessary changes on the hammer so that the Geneva devicewill be rotated one tooth pitch during each operating cycle. It is alsoapparent; that the firearm may be selectively adjusted to dilerentcombinations of bursts by adding to the Geneva device sprocket wheelshaving different amounts of sprockets, as shown by Fig. 7, and by havingcoupler 66 selectively cooperable therewith.

To re the firearm continuously and with trigger control, lever 96 isindexed whereby selector '76 is free of engagement with foot portion 82so that the coupler 66 is biased by spring 72 along shaft 64 to normalposition and arm portion 70 is aligned with spacer 56. Thereby, whentrigger 30 is actuated to tire the firearm, the firearm will continue totire by means of automatic sear 102 until the trigger is released toreleasably hold hammer 24 in cock position, as coupler 66 is free fromblocking engagement with gear wheel 48 or sprocket wheel 54.

When the rearm is to be made inoperative, lever 96 is rotated in acounterclockwise direction to Safe position whereby selector 76 isrotated into position to block counterclockwise rotation of Genevadevice 44 as is best shown in Fig. l. If hammer 24 is in cock positionwhen lever 96 is rotated to Safe position, the camming engagement of theperimeter of cam portion 80 with the adjacent one of the sides 50rotates gear wheel 48 in a clockwise directiom- Consequently, as-cogportion 62'is in engagement with. one of the teeth 52, rotation of gearWheel 48 is transferred to hammer 24 which is retracted thereby fromcock position. If hammer 24 is resting in ring position due to thecomplete expenditure of ammunition or other reasons when lever 96 isrotated to Safe position, such hammer is locked in Safe position afterbeing actuated to retracted action when the firearm is charged.

From the foregoing it is clearly apparent that there is herein provideda novel iiring mechanism whereby an automatic firearm with ahammer-actuated firing pin may be readily regulated for tiring a singleround, bursts of a predetermined number of rounds, and continuously withsuch firing mechanism being simple and rugged in construction andpositive in operation.

Although a particular embodiment of the invention has been described indetail herein, it is evident that many variations may be devised withinthe spirit and scope thereof and the following claims are intended toinclude such variations.

I claim:

1. In an automatic rearm provided with a reciprocal bolt, a firingmechanism including a housing in which there areprovided a hammerpivotal from a firing to a retracted position by the bolt duringmovementthereof from a battery to a recoil position, a trigger mountedrearward of said hammer by means of a transversely disposed pin forpivotal movement between a normal and a retracted position, a selectorarm integral with said trigger and disposed to extend upwardly abovesaid pin rearward of said hammer, a Geneva device rotatably disposedbetween said selector arm and said hammer, a plurality of teeth on saidGeneva device disposed for successive engagement by said hammer torotate said Geneva device a portion of one tooth pitch during movementof said hammer from the retracted to the firing position and theremainder of the tooth pitch during movement thereof from the ring tothe retracted position, a coupler pivotally disposed between saidselector arm and said Geneva device for actuation by said selector arminto position for engagement by one of said teeth to stop rotation ofsaid Geneva device and prevent movement of said hammer to the ringposition when said trigger is in the retracted position thereof and saidhammer engages another one of said teeth.

2. The device as defined in claim 1 wherein said Geneva device includesa gear wheel having said plurality of teeth formed thereon and saidhammer includes a cog disposed thereon to successively engage said teethduring movement of said hammer to 'the ring position for rotating saidgear wheel a part of a tooth pitch, and a lug disposed on said hammerfor successive camming engagement with said teeth during subsequentmovement of said hammer from the tiring position for rotating said gearwheel the remaining portion of the tooth pitch whereby said gear Wheelis rotated one tooth pitch during each operating cycle of the firearm.

3. The device of claim 1 wherein said Geneva device includes a gearwheel provided with a plurality of teeth successively engageable by saidhammer for rotating said Geneva device one tooth pitch during anoperating cycle of the firearm, and a plurality of sprocket wheelscoaxial with said gear Wheel with each of said sprocket Wheels beingprovided with sprockets the number of which on any one of said sprocketwheels being less than that of said teeth, and wherein said coupler isselectively alignable with said gear wheel and said sprocket wheels andpivotally actuatable by said trigger into position to engage theselected one of said gear and sprocket wheels for automatically stoppingthe operation of the firearm after a burst determined by therelationship between the number of said teeth on said gear wheel and thenumber of sprockets on the sprocket Wheel engaged by said coupler.

4. The device of claim 3 including a selector provided 7 with a camhaving steps engageable with said coupler for indexing said selectorinto selective alignment with said gear wheel and said sprocket Wheelsand an outside permeter engageable with said gear Wheel for blockingmovement of said hammer to the firing position to safety the firearmduring any position of said hammer.

S. In an automatic iirearm provided with a reciprocal bolt, a tiringmechanism for selectively regulating the iirearrn to iire a singleround, bursts of a predetermined number of rounds and continuouslycomprising a hammer pivoted from a tiring to a retracted position by thebolt during movement thereof from a battery to a recoil position, atrigger pivotal between a normal and a retracted position, a sear armextending from said trigger for engagement with a catch portion in saidhammer for releasably holding said hammer in a cock position betweensaid retracted and tiring positions, a Geneva device including a gearwheel, a sprocket wheel and a spacer in coaxial relationship, teethionsaid gear wheel numericallyrelated to a fewer number of sprockets onsaid sprocket wheel so 20 engaged by said cog to complete the rotationof said gear Wheel one tooth pitch during subsequent movement of saidhammer to the retracted position, a coupler slidably and pivotallymounted for selective alignment with said gear Wheel, sprocket wheel andspacer and disposed for 'pivotal engagement therewith, a selector membercammingly engaged with said coupler for selectively aligning saidcoupler with said gear wheel, sprocket wheel and spacer and beingselectively engageable with `said gear wheel to block rotation thereoffor safetying the tirearm, and a selector arm on said trigger engageablewith said coupler when said trigger is in the retracted position forpivoting said coupler to blockingly engage the selected sprocket Wheeland gear wheel for blocking rotation of said Geneva device and movementof said hammer to the tiring position.

References Cited in the tile of this patent UNITED STATES PATENTS1,484,163 Vincon Feb. 19, 1924 2,079,039 Razee May 4, 1937 2,532,794Teece Dec. 5, 1950 FOREIGN PATENTS 562,807 Great Britain July 11, 1944

